1. Field of the Invention
The present invention relates to a sealed rechargeable battery and a battery module, in particular, to a sealed rechargeable battery constituted by housing an electrode plate assembly in a metal case having an elliptical or a rectangular cross section and a battery module constituted by connecting the sealed rechargeable batteries in series.
2. Description of Related Art
As a sealed rechargeable battery used as a power source for electric vehicle and hybrid car, a lithium ion rechargeable battery or a nickel metal hydride battery has been put into practical use.
As this type of sealed rechargeable battery, a sealed rechargeable battery having the following structure is conventionally known. As shown in FIG. 12, an electrode plate assembly 54, in which a band-like positive electrode plate 51 and a band-like negative electrode plate 52 are spirally wound with a separator 53 interposed therebetween, is housed in a cylindrical metal case 55 together with an electrolyte solution. A positive electrode tab 56 and a negative electrode tab 57 are extended from the positive electrode plate 51 and the negative electrode plate 52 towards the sides opposite to each other. The negative electrode tab 57, which is downwardly extended, is welded to the bottom face of the case 55, whereas the positive electrode tab 56, which is upwardly extended, is welded to a sealing plate 58 for sealing an opening of the case 55. The sealing plate 58 is fixed to seal the opening of the case 55 with a gasket 59 interposed therebetween.
With the structure as shown in FIG. 12, however, a connection resistance is large because the positive electrode plate 51 is connected to the sealing plate 58 through the positive electrode tab 56 whereas the negative electrode plate 52 is connected to the case 55 through the negative electrode tab 57. As a result, an internal resistance of the battery is increased to degrade the output characteristics and the high-current discharge characteristics. What is worse, since the number of components and the number of assembly steps are both increased, the component cost and the fabrication cost are increased.
Furthermore, since the case 55 is cylindrical, the number of batteries that can be housed in a certain volume is small. Particularly, if a cooling path is formed between the batteries so as to prevent a rise in a battery temperature, the space efficiency is further decreased. Moreover, since the case 55 has a circular cross section, the cooling performance for the central portion of the battery is low, resulting in poor volume efficiency per battery output.
In order to solve the above-mentioned problems, the applicants of the present invention have proposed a battery module having the following structure. A prismatic battery container made of synthetic resin is constituted by integrally connecting a plurality of prismatic battery cases so as to share their shorter side faces. In each battery case, an electrode plate assembly is housed with an electrolyte solution to constitute a cell. Then, the cells are connected to each other in series in the prismatic battery container.
With the prismatic battery container made of synthetic resin, however, it is not possible to perfectly prevent a gas leak from the battery in the long term, resulting in lowered battery performance. Moreover, since the synthetic resin does not have a high thermal conductivity, the cooling efficiency of the battery is low, limiting the increase in output. What is worse, since both sides of the battery container are expanded by an internal pressure generated in each cell, it is necessary to place end plates on both ends of the battery module and to bind the end plates with a rod or a band. As a result, the battery module is increased in size as well as in cost.